Field of the Invention
The present invention relates to a sample spinner for use in NMR spectroscopy and, more particularly, to a mechanism for spinning a sample tube holding a solid sample therein at high speed.
Description of Related Art
When a solid sample is investigated by NMR (nuclear magnetic resonance) spectroscopy, a sample tube holding the solid sample therein is spun while tilted at a given angle (magic angle) to the direction of the static magnetic field. The mechanism used for this purpose is a sample spinner. More specifically, the spinner is installed in the head of an NMR probe. The spinner is inserted as a part of an NMR probe in a bore formed in a static magnetic field generator. The spinner has a transmit/receive coil mounted around a sample tube. When the sample tube is being spun at high speed, the transmit/receive coil generates a varying magnetic field, and an NMR signal is detected.
Each of the spinners disclosed in JP-A-2001-141800 and JP-A-2003-177172 consists of a rotor and a stator. The rotor has a sample tube and an impeller (turbine in JP-A-2001-141800) coupled to the tube. The impeller has a plurality of blades subjected to jet streams of gas. The stator has a plurality of air bearings for holding the rotor in a non-contacting manner. Also, the stator has a plurality of turbine nozzles mounted radially around the impeller to blow jet streams of gas against the impeller. In the spinners disclosed in JP-A-2001-141800 and JP-A-2003-177172, the turbine nozzles are simple holes extending straight. In such a spinner, a gas chamber is formed around the turbine nozzles to feed gas into the nozzles. The gas chamber assumes a simple annular form. The turbine nozzles are connected to the gas chamber perpendicularly or nearly perpendicularly.
The spinner disclosed in U.S. Pat. No. 5,202,633 has a plurality of turbine nozzles each having a linear shape. The cross-sectional area of each turbine nozzle continuously decreases along the direction of flow of gas. The gas chamber formed around the turbine nozzles is formed as a simple annular cavity. FIG. 5 of U.S. Pat. No. 5,202,633 shows tilted turbine nozzles that create oblique jet streams.
In order to perform high-resolution measurements, it is necessary to increase the spinning rate of the sample tube as high as possible. That is, the speed or power of jet streams needs to be increased to a maximum. However, when gas is admitted into the spinner, if the gas pressure is simply increased, and if the flow of the gas inside the spinner is disturbed hydrodynamically, e.g., contracted flow and peeling occur, the pressure loss will increase. As a result, it would be difficult to increase the spinning rate of the sample tube.
It can be said that sufficient structural consideration has not been given to reduce the pressure loss throughout the gas channel of the conventional spinner including the gas chamber and turbine nozzles. Consequently, it has been difficult to increase the upper limit of the spinning rate.